ath11k: fix vht guard interval mapping

Guard interval value which comes from VHT_SIG_A TLV has a mapping
where value 0 corresponds to LGI, 1 and 3 corresponds to SGI.

Value 3 which is SGI(0.4us) in VHT was incorrectly mapped to a GI
of 3.2us(only applicable in HE) resulting in incorrect rx GI stats.
Fixing the mapping.

Signed-off-by: Manikanta Pubbisetty <mpubbise@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>