dt-bindings: net: qcom,ipa: do not override firmware-name $ref

dtschema package defines firmware-name as string-array, so individual
bindings should not make it a string but instead just narrow the number
of expected firmware file names.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20240129142121.102450-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>