staging: fbtft: fix strncmp() size warning

staging: fbtft: fix strncmp() size warning

strncmp() stops comparing when either the end of one of the first two
arguments is reached or when 'n' characters have been compared, whichever
comes first.That means that strncmp(s1, s2, n) is equivalent to
strcmp(s1, s2) if n exceeds the length of s1 or the length of s2.

This patch avoids that the following warning is reported by smatch:

drivers/staging/fbtft/fbtft_device.c:1458
 fbtft_device_init() error: strncmp() '"list"' too small (5 vs 32)

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>