srsenb_sib.conf: Fix warning about wrong prach_freq_offset value

WARNING: Invalid PRACH configuration - prach=(2, 8) does not fit into the eNB PRBs=(0, 6).
       Consider changing the "prach_freq_offset" value to 0 in the sib.conf file when using 6 PRBs.

Change-Id: Ie4374faca62a4d0289f78674eadec7eb5d045dfd
1 file changed