check-package: Flag usage of '\t \\$'.

check-package: Flag usage of '\t \\$'.

check-package would flag tabs before a backslash ('\t\\'),
two spaces before a backslash ('  \\') but would not flag a tab before space
before backslash ('\t \\'), allowing someone to bypass the check.

Signed-off-by: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>
Reviewed-by: Ricardo Martincoski <ricardo.martincoski@datacom.ind.br>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>