hidraw: fix number of bytes to copy from uevent in parse_uevent_info

Commit 5c9f147 (libusb#432) replaced a call to strdup with an explicit
memcpy to a buffer on the stack.

However, it incorrectly used the buffer size, instead of the clamped
uevent length, as the argument to memcpy, resulting in reads past the
end of uevent:

$ valgrind -q hidtest/hidtest_hidraw 1>/dev/null
==51900== Invalid read of size 8
==51900==    at 0x48571D5: parse_uevent_info (hid.c:496)
==51900==    by 0x48574F2: create_device_info_for_device (hid.c:578)
==51900==    by 0x4857ED7: hid_enumerate (hid.c:876)
==51900==    by 0x1094CE: main (test.c:105)
==51900==  Address 0x4b6c1a0 is 7 bytes after a block of size 185 alloc'd
==51900==    at 0x4846CC3: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==51900==    by 0x4AA0E45: UnknownInlinedFun (fileio.c:534)
==51900==    by 0x4AA0E45: read_virtual_file_at.constprop.0 (fileio.c:572)
==51900==    by 0x4A9D37C: UnknownInlinedFun (fileio.h:74)
==51900==    by 0x4A9D37C: UnknownInlinedFun (fileio.h:77)
==51900==    by 0x4A9D37C: sd_device_get_sysattr_value (sd-device.c:2318)
==51900==    by 0x4A8B0D1: udev_device_get_sysattr_value (libudev-device.c:747)
==51900==    by 0x48574BE: create_device_info_for_device (hid.c:578)
==51900==    by 0x4857ED7: hid_enumerate (hid.c:876)
==51900==    by 0x1094CE: main (test.c:105)
==51900==

Fix this by using uevent_len as the argument to memcpy.

Calling strndupa was considered but abandoned, as it is not standard.

Fixes: 5c9f147 (libusb#432)
Fixes: 4779d63

linux/hid.c

@@ -493,7 +493,7 @@ static int parse_uevent_info(const char *uevent, unsigned *bus_type,
 	size_t uevent_len = strlen(uevent);
 	if (uevent_len > sizeof(tmp) - 1)
 		uevent_len = sizeof(tmp) - 1;
-	memcpy(tmp, uevent, sizeof(tmp));
+	memcpy(tmp, uevent, uevent_len);
 	tmp[uevent_len] = '\0';
 
 	char *saveptr = NULL;