checkpatch: improve the compatible vendor match

Improve the vendor name match in vendor-prefix.txt by only matching the
exact vendor name at the beginning of lines.

Change-Id: Iecabd626e8a68c0e64929ea2c2985c015595efb2
Signed-off-by: Florian Vaussard <florian.vaussard@epfl.ch>
Cc: Joe Perches <joe@perches.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: cc93319b5f2471ff2042ce62ea6da1f3bb3ce394
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>