isofs: fix timestamps beyond 2027

commit 34be4dbf87fc3e474a842305394534216d428f5d upstream.

isofs uses a 'char' variable to load the number of years since
1900 for an inode timestamp. On architectures that use a signed
char type by default, this results in an invalid date for
anything beyond 2027.

This changes the function argument to a 'u8' array, which
is defined the same way on all architectures, and unambiguously
lets us use years until 2155.

This should be backported to all kernels that might still be
in use by that date.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>