ath11k: Fix memory leak on error path

In ath11k_mac_setup_iface_combinations(), if memory cannot be assigned
for the variable limits, then the memory assigned to combinations will
be leaked. Fix this.

Addresses-Coverity-ID: 1497534 ("Resource leaks")
Fixes: 2626c269 ("ath11k: add interface_modes to hw_params")
Signed-off-by: Alex Dewar <alex.dewar90@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201004100218.311653-2-alex.dewar90@gmail.com