media: saa7134-input: improve error handling

Currently, the code produces those false-positives:
	drivers/media/pci/saa7134/saa7134-input.c:203 get_key_msi_tvanywhere_plus() error: uninitialized symbol 'b'.
	drivers/media/pci/saa7134/saa7134-input.c:251 get_key_kworld_pc150u() error: uninitialized symbol 'b'.
	drivers/media/pci/saa7134/saa7134-input.c:275 get_key_purpletv() error: uninitialized symbol 'b'.

Improve the error handling code, making it to look like our
coding style.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>