package/mtd: fix build without openssl

Add a patch that removes dependency on openssl header when openssl is
not installed.

Fixes:
http://autobuild.buildroot.net/results/a78/a78544def5c17edccdf5db821318b8efa3fc7b8f/
http://autobuild.buildroot.net/results/ed8/ed82ef6c15d7f59c9b93d237f53fc09513ed5c4f/
http://autobuild.buildroot.net/results/ede/ede17d68948fd478c366673b7d22f07cee3bd09a/



Cc: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>