nvramtool: fix getopt handling with unsigned char

make failed while executing "OPTION     option_table.h" by printing
nvramtool's usage message when crosscompiling coreboot on the BBB.
The reason is the usage of char for the return value of getopt instead
of int and comparing it to -1 later... although char might be unsigned
as it is usually on ARM.

Change-Id: Ib20fd5ef174d484bbb35f80150b8f898d95d0fe4
Signed-off-by: Stefan Tauner <stefan.tauner@gmx.at>
Reviewed-on: http://review.coreboot.org/9307
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
1 file changed