power: smb5-lib: Fix rejection of valid QC4.0 and USB-PD voltages

Currently in QC4.0 and in USB-PD, attempts to set adaptor voltages other
than 5, 9 or 12V are rejected because of incorrect logic in the function
that sets switching frequency. Fix this so that all valid voltages are
supported.

CRs-Fixed: 2310688
Change-Id: I55095e19559aeffed97fa7206a09b1cfd9c7ffd5
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>