Add pin 21 ground pad.
Prior to fixing, violations were:
checking component: Si4362
Violating Rule 3.8
Description and keywords properties contains information about the component.
Violating EC01 - Extra Checking
Check pins names against pin types.
Violating EC03 - Extra Checking
Check part reference, name and footprint position and alignment
Violating EC04 - Extra Checking
Check line width and background for box outlines parts.
Violating EC05 - Extra Checking
Pin numbers should not be duplicated, and all pins should be present
Pin 4 is missing
Pin 5 is missing
Pin 7 is missing
Signed-off-by: Andrew Bradford <andrew@bradfordembedded.com>