firmware-utils: mkdapimg: fix compiler warnings/errors

firmware-utils: mkdapimg: fix compiler warnings/errors

mkdapimg.c:162:48: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
mkdapimg.c:206:48: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
mkdapimg.c:209:49: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
mkdapimg.c:211:51: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
mkdapimg.c:162:7: error: ignoring return value of ‘fread’, declared with attribute warn_unused_result [-Werror=unused-result]
/usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error: ‘__builtin___strncpy_chk’ output may be truncated copying between 0 and 20 bytes from a string of length 30 [-Werror=stringop-truncation]
/usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ output may be truncated copying 20 bytes from a string of length 20 [-Werror=stringop-truncation]
/usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ output may be truncated copying 30 bytes from a string of length 30 [-Werror=stringop-truncation]
mkdapimg.c:216:7: error: ‘ofile’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
mkdapimg.c:225:2: error: ‘ifile’ may be used uninitialized in this function [-Werror=maybe-uninitialized]

Signed-off-by: Petr Štetiar <ynezz@true.cz>