According to AM572x DM SPRS953A, QSPI bus speed can be 76.8MHz, hence
update QSPI input clock divider value (DPLL_PER_HS13) to provide 76.8MHz
clock, so that driver can use the same.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>