iwlwifi: dbg_ini: allocate dram buffer with proper flags

Use the same flags we use in the legacy buffer allocation.
Missing __GFP_NOWARN will cause an unwanted warning incase
we fail to allocate.
Missing __GFP_ZERO will give a buffer initially filled with
garbage which can make debug difficult in case our wrap count is zero.

Signed-off-by: Shahar S Matityahu <shahar.s.matityahu@intel.com>
Fixes: d47902f9 ("iwlwifi: dbg: add apply point logic")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>