Make the inputStyle as Object Rather than String

[TheAvtarSingh]

• Steps to reproduce the issue:
  <OtpInput
  value={otp}
  onChange={setOtp}
  inputStyle={}
  numInputs={4}
  renderSeparator={-}
  renderInput={(props) => <input {...props} />}
  />
  JSX attributes must only be assigned a non-empty 'expression'.ts(17000)

• Relevant error messages and/or screenshots: